This invention relates to the art of solar energy collectors, and more particularly to an improved absorber plate.
In the past solar energy collector panels have been made with various structures. An example of one structure is illustrated in U.S. Pat. No. 3,039,453 wherein the absorber plate is formed from a metallic plate which has had grooves crimped into its surface for receiving a flexible plastic tubing that would be snapped into these grooves. The configuration of these grooves is substantially circular in cross section and is greater that 180.degree. in circumference. This allows the flexible tubing to be retained in the grooves without the use of additional fastening means if desired. This type of absorber plate structure has also been utilized with metallic tubing. However, in both instances the structure has proved to have limitations. The major problem results from the fact that the absorber plate, when it is heated by the sun's rays will cause the metal of the absorber plate to expand which causes the grooves to expand, causing them to loosen their grip on the tubing snapped therein. While the absorber plate metal is expanding, the tubing, even when it is metallic, is not expanding due to the fluid flowing therethrough which keeps the tubing relatively cool. When the grip of the grooves on the tubing has been relaxed, the efficiency of the solar energy collector panel is greatly reduced due to the lowered conduction rate of the heat from the absorber plate to the tubing.
Some additional draw-backs to the above described absorber plate results from the fact that the continued heating and cooling of the metallic absorber plate will eventually result in fatigue of the metal around the gripping portions of the grooves. When this occurs there will be a loss of conduction in the efficiency of the solar energy collector panel. Another draw-back to the structure of the absorber plate described above relates to the fact that the groove of the absorber plate is gripping the tubing around far less than its 360.degree. of circumference. Maximum efficiency would occur where the groove contacts the tubing around its entire surface.
Another problem in prior absorber plate constructions has resulted from the use of a plurality of absorber plate sections to form the absorber plate. These absorber plate sections have inter-locking structure along their lateral edges that allow for a sliding connection to be made in the absorber plate sections. This sliding-type connection between the adjacent absorber plate sections has been necessary in order to allow for heat expansion of the metal of the absorber plate sections. A draw-back to this construction, however, is the fact that it does not provide a 100% seal against water and therefore the absorber plates formed in the manner described cannot be used as a roof structure by itself, but would require some type of a cover panel.
A further disadvantage of prior solar energy collector panels has resulted when it is necessary to have a large absorber plate. In the past it has been necessary to use a large number of solar energy collector panels that would be placed side by side and inter-connected. The resulting wall section of these solar energy collector panels make the structure more expensive than it need be.
Electrolysis resulting from the use of dis-similar metals for the absorber plate and the tubing has also been a prior problem. The cost of making the absorber plates from copper so that they would be made from the same metal tubing is prohibitive. In an effort to cut down on the electrolysis problem, some solar energy collector structures use a paint on the surface of the tubing but this results in a lower conduction efficiency. Another problem that has resulted from prior solar energy collector panels that utilize a plurality of absorber plate sections has been the fact that many of these structures lack conductance across their entire absorber plate assembly. In many instances it is difficult to have an even flow of fluid through all of the tubing members which may result from different pressures in the system or due to some of the tubes being partially or fully clogged. When these instances occur whole sections of the absorber plate assembly may be transferring only a small portion or none of the heat which has been collected on these absorber plate sections.